مجله پژوهش آب ایران
پیاپی 6 (بهار و تابستان 1389)

Permanent control of embankment dam stability during construction especially in the instance of first impounding as well as during the project life is a significant issue. The role of clay core in such dams is to prevent water leakage. Rapid construction of a clay core causes pore water pressure to be increased and effective stress to be reduced. This may endanger the stability of dam. Hence, instrumentation of such dams, to monitor their behavior, plays an important role in the dam stability. An earth dam is a continuous structure with non-linear behavior which can be anlysed by finite element method and an appropriate soil model. In this paper, induced stresses and also settlement of a dam during construction obtained from the instrumentation of Nahreyn dam have been compared with the analytical results obtained from a finite element method. Mohr-Coulomb and hardening soil models were used to do stress-strain analysis. It is shown that instrumentation data and the analysis results are in good agreement and that the dam stability during construction and afterwards could be controlled using strength soil parameters and above-mentioned soil models.

Models can be calibrated using suitable field data. A coupled volume balance–zero inertia (VB-ZI) model increases the accuracy of advance distance estimation in furrow irrigation. Surface storage volume in VB-ZI model was estimated using a power function. In this research the subsurface storage in furrow irrigation was calculated using the corrected Hall technique and a modified VB-ZI model (MVB-ZI) was developed. The developed model uses the momentum term of the ZI model. For evaluation of the MVB-ZI accuracy in furrow irrigation, three data series in different field conditions were used. The collected field data were hydraulics and geometric coefficients of cross section, advance time, inflow and outflow discharge, Manning’s coefficient, furrow bed slope and infiltration coefficients. The root mean squared error (RMSE) index, coefficient of residual mass (CRM) index and model efficiency (ME) index were used to evaluate the model. The RMSE values for the MVB-ZI model were 26.57, 12.71 and 20.49 for data series 1, 2 and 3, respectively. The calculated values for VB-ZI model were 30.13, 16.63 and 22.48. The CRM values for field data series 1, 2 and 3 were 0.217, 0.272 and 0.303, respectively which indicate the MVB-ZI model overestimation. The results show that the MVB-ZI model accuracy in estimating advance distance in furrow irrigation is greater than that of the VB-ZI and VB models. Therefore, the use of MVB-ZI model is recammended because of its simplicity and accuracy compared with VB-ZI and VB models.

The raindrops cause dispersion of soil particles when they hit the ground and accelerate the process of water erosion. The intensity and amount of soil dispersion depends on kinetic energy which, in turn, is influenced by rainfall intensity. To investigate the relationship between the amount of splash erosion and rainfall intensity at meteorology stations of Kurdistan province, sprinkling cups were designed and installed in these stations. The displaced sands at given time intervals were measured. The rainfall intensity at the time intervals was extracted from related graphs and using Wieshmaier's formula, kinetic energy of rain was calculated. The results showed that the relationship between rainfall intensity and splash rate in Marivan station was more strong whereas nosignificant relationship was observed in Saghez station.

This paper studies the hydraulic performance of rice husk envelope in subsurface drainage system in Behshahr, Iran. Seven piezometers were installed between two subsurface drains designated as S3PD14 and S3PD15. Subsurface drainage system was monitored in rainy season. Parameters such as daily midpoint depth of water table, drain discharge rate, and head loss of water table in the vicinity of the drain including approach-flow head (hap) and entrance-flow head (he) were recorded. Parameters such as approach-flow resistance (Wap), approach-flow constant (αap) and approach-flow head loss fraction (Fap) were estimated in both S3PD14 and S3PD15 drains. The results showed that the performance of rice husk was better in S3PD15. Also, the proper performance of rice husk depends on the rate of envelope decay and the installation conditions of the trench backfill, which is reflected in its hydraulic conductivity. The great difference between approach-flow head and entrance-flow head could be related to clogging of the external part of rice husk envelope.

In the present study, the effect of application of a zeolite (Mianeh clinoptilolite), was investigated on the moisture contents and soil characteristic curves of a sandy and a clay loam soil. Mianeh clinoptilolite zeolite was applied to soils at four levels (0, 2, 5, and 8% on weight basis) in a completely randomized experiment. Soil’s moisture content was determined at suctions of 0, 5, 7.5, 10, 33, 100, 500, and 1500 kPa using hanging water columns and pressure plate apparatus. Water retention curve models of van Genuchten (1980), Brooks-Corey (1964), and Campbell (1974) were fitted to each soil data using SWRC 3.0 software. Mianeh zeolite enhanced soil moisture content at each measured soil suction. The Mianeh zeolite increased the saturation and available water content of the sandy soil and saturation water content (qs) and residual water content (qr) in both soils. In addition, this zeolite modified the shape of moisture characteristic curves of both soils and influenced the parameters of all three water retention models in a manner exhibiting reduced water release rates. Mianeh zeolite can be useful in enhancing water use efficiency.

In this study, the agro-hydrological model SWAP 3.03 was used for prediction of wheat (Rowshan variety) production under different qualities of irrigation water (1.4, 4.5 and 9.6 dS/m) obtained from three local wells which were used in a factorial plot design with four levels of water depth (50, 75, 100 and 125% of ETc) during 2005-2006 growing season in the Research Field of Birjand University. The model was initially calibrated for crop coefficients of winter wheat based on a study in South Khorasan province. Predicted results directly followed the trend of actual crop production for various amounts and qualities of irrigation water. Predicted and actual crop production was statistically significant at 1% level with an R2 of 0.83. Average yield of Rowshan variety was 10% lower, as compared with theactual yield. However, such differences were not found to be significantly different based on average t-test.

In conventional drainage system, water level in the plant root zone is lowered and salt in the irrigated area is washed away to the drain and transferred to another area. Controlled drainage is one of the management methods to control water level below the depth of the growing root zone. Discharging low-quality drainage water into other areas may have a devastating impact on the environment of many water habitats. In water table control methods, water loss from the region is reduced which means that more water can be used by soil. It is argued that the depth and quality of water table are effective in the growth and expansion of aerial branches of roots, quantity of the produce, reduction of drainage water and water Use efficiency. In order to determine these effects, a physical simulation model (lysimeter) was used to evaluate the impact of controlled drainage system and irrigation on water salinity of sorghum crop compared with free drainage. For this purpose, two treatments of drainage water level (free drainage (FD) and controlled drainage (CD)) and three treatments of irrigation water salinity (0.75 dS m-1, 3.4 dS m-1 and 4.8 dS m-1) with in three replications using18 lysimeters were employed. The results of the experiments show that unlike free drainage conditions in which soil moisture would be supplied only through irrigation and thus the sorghum plant will encounter shortage of moisture in the soil before the next irrigation,, in controlled drainage treatments soil moisture is supplied through capillary, water absorption is provided by the plant in potential level, which leads to increase of yield amounting to 3.5 time more than the free drainage. Moreover controlled drainage treatments could supply almost one third of needed water through water table. Therefore it is said that drainage water is diminished in this system at the same ratio. The mutual effect of water table and irrigation water salinity shows that higher moisture conditions in controlled drainage treatments will diminish the effect of salt accumulation in comparison to free drainage conditions; therefore irrigation water salinity has not made its real effect.

Water deficiency is one of the limiting factors in canola (Brassica napus L.) production in arid and semi-arid regions. Past researchers have shown that potassium increases plant resistance to water stress. This study was conducted to assess the simultaneous effects of water stress and application of different levels of potassium fertilizer on canola in the field of Agriculture and Natural Resources Research Center of Shahrekord. For this purpose, a split-plot experiment in randomized complete block design was carriedout with three replicates. The main plots were three levels of drought stress including: I1: irrigated with full level of water requirement during plant growth stages with 5690 m3/ha, I2: irrigated with 85% of water requirement in stemming, flowering and podding stages, and I3: irrigated with 70% of water requirement in flowering and podding stages. The sub plots were five levels of potassium fertilizers including K1=control, K2=0/75R, K3=1R, K4=1/25R and K5=1/5R (R=fertilizer recommendation based on soil testing). Means comparison were conducted with Duncan test at 5 percent level. Results show that irrigation treatments had significant effects on straw yield and total yield. Potassium treatments had significant effects on all characteristic except on pod length, grain oil percentage and potassium percentage in shoot. Potassium fertilizer application did not have any significant differences on some of growth indices but it slightly decreased the negative impacts of water deficiency. Thus, based on the results of this research, in deficit irrigation condition, the best treatment with high yield is I3K3 treatment.

Aggregation of cohesive sediments increases the rate of sediment deposition. To investigate the cohesive sediment deposition processes, experiments were conducted in a rotational flume in the Hydraulic Laboratory of Shahrekord University. Sediment samples were taken from a small dam reservoir located near Shahrekord city (as a subbasin of north Karun watershed). The sediments were composed of 31% clay, 58% silt and 11% sand. For each experiment, the velocity and shear stress profiles were measured using acoustic doppler velocimeter (ADV) and suspended sediment concentration was measured using drying and weighting method. Duration of each experiment was 180 minutes and the required time to reach the equilibrium concentration ranged from 30 to 60 minutes. The results show that a linear relationship exists between the bed shear stress and the relative equilibrium concentration. Based on the time variations of the sediment concentration, the deposition rate of the sediments was calculated and a parabolic relationship was derived between the deposition rate of sediments and the equilibrium relative concentration. The threshold of non-settling of sediments has also been investigated. Minimum bed shear stress at threshold deposition of sediment for initial sediment concentration of 5, 10 and 20 gm/l were 0.827, 0.938 and 0.98 N/m2, respectively. This means that the minimum shear stress directly depends on the initial concentration of the sediment.

Agriculture sector is one of the major users of water in Kerman. In this study, economic value and demand function of water for sugar beet production in Kerman is estimated. The required data was collected by filling 130 questionnaires from producers. Results show that water is the most effective input in producing sugar beet by an estimated coefficent of 0.25. therfore, it has the greatest impact on studied inputs. Also, price elasticity of water demand itself is less than minus 1, which shows that pricing policy is a main factor in controlling non-optimum use of water. The real price of water to produce sugar beet is estimated to be 705 Rials per cubic meter wich292.39 rials higher than the market price. It is suggested that estimated price gap be set as a basic price in order to apply water pricing policy to control incorrect use of water.

In the present study severity, duration and frequency of droughts were analyzed using monthly rain data in Lorestan province. At first, the rainfall data was normalized and then rain time series Z score was created. Dry months and periods were separated by applying run theory and by determining critical. Threshold Then, the severity, duration and frequency (SDF) curves of the droughts were plotted. By applying Markov chain, transition probability matrix and region’s static probability matrix were extracted and the number of dry years and duration of the droughts in the region was forcasted for the next 15 years.

Several studies confirm the negative effects of non- uniform distribution of water on crop productivity and deep percolation. This means that some parts of the farm get more water than required on the other hand, other parts of the farm suffer from under- irrigation and water stress. In this research, the best fit functions for prediction of Uniformity Coefficient and Distribution Uniformity obtained using 20 randomly selected pressure conduit irrigated farms in Dehgolan plain (10 classic sprinkler systems and 10 wheel move systems). The measured Uniformity Coefficient and Distribution Uniformity were compared by fitting normal, uniform and beta distributions functions. The results show that normal distribution has the best fit line in predicting the Uniformity Coefficient and Distribution Uniformity in all the 5 settlements in the10 wheel move farms with spacings of 9, 12, 15, 18 and 21 meters as well as in the 10 farms with classic sprinkler systems,. In all of three cases, normal distribution functions have the most accuracy in prediction of Uniformity Coefficient and Distribution Uniformity. Also the accuracy increased in wheel move system with decreasing the space between two frequent settlements.